Method for controlling a regeneration valve of a fuel vapor retention system

ABSTRACT

The invention relates to an operating method for a regeneration valve of a fuel vapor retention system, particularly of a tank vent valve for regenerating an activated carbon filter during which the regeneration valve is controlled by a control signal, whereby the control signal corresponds to a designated valve position of the regeneration valve. The invention provides that the correlation between the control signal and the resulting valve position of the regeneration valve is determined during a calibration process.

CROSS REFERENCE TO RELATED APPLICATION

This application is the US National Stage of International ApplicationNo. PCT/DE2003/003272, filed Oct. 1, 2003 and claims the benefitthereof. The International Application claims the benefits of GermanPatent application No. 10252826.8 DE filed Nov. 13, 2002, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a method for controlling a regeneration valveaccording to the preamble of the claims.

BACKGROUND OF THE INVENTION

Modern motor vehicles with spark ignition engines have a fuel tank inwhich the fuel vapors which are emitted while standing still arecollected by an activated carbon filter in order to prevent damage tothe environment. However, such activated carbon filters only have alimited capacity and must therefore be regenerated while operating inorder to subsequently again be able to absorb fuel vapors. Thisregeneration of an activated carbon filter takes place by flushing withfresh air in which case the fuel vapors collected in the activatedcarbon filter are released. For this purpose, the activated carbonfilter is connected to the intake pipe of the spark ignition engine viaa controllable tank vent valve in such a way that the spark ignitionengine takes in fresh air through the activated carbon filter in thecase of an open tank vent valve and as a result regenerates theactivated carbon filter.

While an activated carbon filter is being regenerated, the fuel vaporsflushed from the activated carbon filter get into the intake pipe of thespark ignition engine and as a result change the ratio of the mixtureand the filling ratio causing an increase in the engine torque.

While such spark ignition engines are being operated, this disturbinginfluence of regenerating an activated carbon filter can be compensatedfor by regulating it, for example, by changing the throttle valveposition accordingly or adjusting the ignition angle.

However, if such a spark ignition engine is operated dynamically, it isoften not possible to carry out such a regulation with a view tocompensating for the disturbing influence so that as a result acorrection via a suitable control system takes place. In this case thecontrol system is based on a physical model which requires knowledge ofthe valve characteristic of the tank vent valve. The correlation betweenthe pulse-width modulated control signal for the tank vent valve and thecorresponding valve position of the tank vent valve is thereforedetermined by the manufacturer in the case of the known control systemsand stored in a performance graph in such a way that the control systemcan fall back on the stored correlation between the control signal andthe associated valve position while operating in order to compensate forthe disturbing influence of regenerating an activated carbon filter bymeans of a suitable control system.

A disadvantage of this known method is the fact that the correlationbetween the pulse-width modulated control signal for the tank vent valveand the resulting valve position can be subject to fluctuations in whichcase the fluctuations are based on manufacturing tolerances,contamination and ageing effects as well as on temperature influences.As a result, the conventional control system with a view to compensatingfor the disturbing influence of regenerating an activated carbon filtertherefore functions unsatisfactorily.

The publication U.S. Pat. No. 5,216,991 discloses a method forcontrolling a regeneration valve of a fuel vapor retention system for aninternal combustion engine in the case of which the regeneration valveis controlled with a control signal, whereby the control signalcorresponds to a designated valve position of the regeneration valve andthe correlation between the control signal and the resulting valveposition of the regeneration valve is determined during a calibrationprocess.

SUMMARY OF THE INVENTION

Therefore, it is the object of the invention to create a method forcontrolling a tank vent valve which makes possible a better compensationfor the disturbing influence of regenerating an activated carbon filter.

Taking a known method for controlling a tank vent valve as the startingpoint, this object of the invention is achieved according to thepreamble of the claims by the characterizing features of the claims.

The invention includes the general technical teaching that thecorrelation between the control signal for the tank vent valve and theresulting valve position while operating is determined within theframework of a calibration process. Thus, the regeneration valve iscontrolled sequentially with different values of the control signal. Thespeed and/or the air ratio of the internal combustion engine isregulated to predetermined desired values in the case of each value ofthe control signal and the engine interventions required for this aredetermined. The valve position of the regeneration valve is derived fromthe engine intervention for each value of the control valve. Theindividual value of the control signal and the resulting valve positionare then also stored as support points of a valve characteristic. Thisoffers the advantage that ageing and contamination effects,manufacturing tolerances as well as temperature fluctuations are takeninto consideration, which leads to a more accurate determination of thecorrelation between the control signal and the resulting valve position.When regenerating the activated carbon filter, the disturbing influenceof the fuel vapors flushed from the activated carbon filter can then becompensated for in a better way.

The calibration process according to the method of the invention ispreferably carried out while the internal combustion engine is idling inwhich case the disturbing influence of the fuel vapors flushed from theactivated carbon filter is preferably already compensated for by theexisting regulations.

For example, the idling speed can be measured and regulated at apredetermined desired value by means of engine intervention. The fuelvapors flushed from the activated carbon filter when it is regeneratedthen first of all increase the engine torque and the resulting speed, inwhich case this disturbance variable is again controlled by the engineintervention as a result of which the idling speed is stabilized.

However, it is also possible that during calibration, the air ratio ofthe exhaust gas of the internal combustion engine is measured andregulated to a predetermined desired value. The fuel vapors flushed fromthe activated carbon filter during regeneration then first of all changethe ratio of the mixture in the intake tract of the internal combustionengine, thereby changing the air ratio of the exhaust gas. This changingof the air ratio by regenerating the activated carbon filter is thencompensated for by a suitable engine intervention as a result of whichthe air ratio is stabilized.

The degree of the engine intervention required while the activatedcarbon filter is being regenerated in order to control the disturbancevariable is, in this case, a measure for determining the volume offlushed fuel vapors and therefore allows a conclusion to be drawn aboutthe valve position of the tank vent valve. If, for example, an extensiveengine intervention is required in order to control the disturbancevariable when the activated carbon filter is regenerated, then this isbased on a correspondingly high mass or volume flow from the activatedcarbon filter which is only possible in the case of a tank vent valvewhich is open accordingly wide. However, if on the other hand, no oronly a slight engine intervention is required to control the disturbancevariable while the activated carbon filter is being regenerated, thenthis as a result means that the tank vent valve is closed or only openedslightly so that only a slight mass or volume flow is extracted or drawnoff from the activated carbon filter in the intake tract of the internalcombustion engine.

The engine intervention to compensate for the regeneration of theactivated carbon filter during calibration can include differentmeasures which can be used alone or in combination with one another.

For example, the throttle valve position can be changed in order tocompensate for the fuel vapors flushed from the activated carbon filterduring regeneration. In this way, the throttle valve can be closedcompletely or partially while the activated carbon filter is beingregenerated so that the sum total of the mass or volume flow sucked inor drawn in via the throttle valve and the mass or volume flow flushedfrom the activated carbon filter while the activated carbon filter isbeing regenerated remains as constant as possible.

In addition, the engine intervention with a view to compensating for thefuel vapors flushed from the activated carbon filter during regenerationalso consists of the fact that the ignition angle must be adjusted inorder to change the engine torque accordingly. If, for example, the tankvent valve is opened completely, then a relatively large volume of fuelvapor flows into the intake tract of the internal combustion engine as aresult of which the filling ratio and therefore the engine torque areincreased. The ignition angle can then be retarded in order to reducethe engine torque accordingly.

The invention does not necessarily require a complete determination ofthe valve characteristic of the tank vent valve. However, it is alsopossible that only individual support points of the valve characteristicare determined.

Of particular importance in this case is the opening point of the tankvent valve, i.e. the control signal in the case of which the tank ventvalve opens. In order to determine this opening point, the engineintervention can be compared to a predetermined limiting value. If thedegree of the engine intervention required with a view to compensatingfor the fuel vapor flushed from the activated carbon filter exceeds thelimiting value it can be assumed that the tank vent valve is open. If,on the other hand, the degree of the required engine intervention isbelow the limiting value then this indicates that the tank vent valve isclosed.

If the engine intervention consists of changing the throttle valveposition, then the angle of change of the throttle valve positionrequired for the compensation process can be compared to the limitingvalue in order to determine the opening point of the tank vent valve.

If, on the other hand, the engine intervention includes an adjustment ofthe ignition angle, then the change of the ignition angle required forthe compensation process can be compared to the limiting value in orderto determine the opening point of the tank vent valve.

In order to determine the opening point of the tank vent valve, thecontrol signal for the tank vent valve can then be increasedprogressively until the said comparison of the engine intervention tothe predetermined limiting value shows that the tank vent valve hasopened. It is then possible to derive the associated valve position fromthe engine intervention required for this as has already been explainedabove.

In this way it is also possible to determine, in addition to the openingpoint, further support points of the valve characteristic. For thispurpose, further values of the control signal are set progressively forthe tank vent valve while the engine intervention, which is required tocompensate for the fuel vapors flushed from the activated carbon filter,is determined in each case. It is then possible to derive the associatedvalve position from the engine intervention as has already beenexplained above. In this way, it is then possible to determine severalsupport points of the valve characteristic in which case each supportpoint consists of one value of the control signal for the tank ventvalve and the valve position.

The control signal for the tank vent valve is preferably a pulse-widthmodulated electrical signal in which case the pulse width determines thevalve position of the tank vent valve. However, within the framework ofthe invention it is also possible to use another control signal such asa pulse-amplitude modulated signal instead of a pulse-width modulatedsignal.

In addition, the invention is not limited to tank vent valves for thespark ignition engines mentioned at the beginning, but can also be usedin other internal combustion engines that are operated with volatilefuels.

In addition, the invention is not limited to fuel supply systems with anactivated carbon filter for storing the fuel vapors which are emitted.However, it is also possible to use another component instead of anactivated carbon filter, said component absorbing the fuel vapors whichare emitted from the fuel tank in order to prevent damage to theenvironment.

Moreover, the invention is not limited to fuel supply systems in whichthe tank vent valve is arranged between the intake tract of the internalcombustion engine and the activated carbon filter. In general, theinvention also includes a method for controlling a regeneration valve ofa fuel vapor retention system in the case of which the regenerationvalve can also be arranged in another place within the fuel supplysystem.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantageous further developments of the invention are included inthe subclaims or are explained below on the basis of the accompanyingdrawings. They are as follows:

FIG. 1—a fuel supply system of an internal combustion engine with anexhaust gas catalytic converter,

FIG. 2 a-2 c—the method according to the invention in the form of a flowchart as well as

FIG. 3—a characteristic of a vent valve.

DETAILED DESCRIPTION OF THE INVENTION

The representation in FIG. 1 shows an internal combustion engine 1 withan injection system in which case the internal combustion engine 1 isconstructed in a conventional way and is therefore only showndiagrammatically.

The internal combustion engine 1 is controlled by an electronic controlunit 2 in which case the control unit 2, for example, specifies themoment of injection as well as the duration of injection of theinjection system.

The control unit 2 evaluates the measuring signals of a mass air flowsensor 3 as well as a lambda sensor 4 as input signals, in which case,the mass air flow sensor 3 is arranged in an intake tract 5 of theinternal combustion engine 1 while the lambda sensor 4 is located on theoutlet side of the internal combustion engine 1 in an exhaust gas duct6.

In addition, a throttle valve 7 is also arranged in the intake tract 5of the internal combustion engine 1, said throttle valve controlling themass air flow sensor sucked in or drawn in by the internal combustionengine 1 and is set by means of the control unit 2.

Moreover, a conventional three-way catalytic converter 8 is arranged inthe exhaust gas duct 6.

A fuel tank 9 is provided for the fuel supply which is connected to theinternal combustion engine 1 via a fuel line 10 which is only showndiagrammatically.

In addition, the fuel tank 9 has a vent line 11 which opens into anactivated carbon filter 12, in which case the activated carbon filter 12can store intermediately the fuel which is emitted from the fuel tank 9.This prevents fuel which is emitted from escaping from the fuelcontainer 9 which would contaminate the environment.

However, the activated carbon filter 12 only has a limited storagecapacity and must therefore occasionally be flushed with ambient air inorder to flush the stored fuel from the activated carbon filter 12.Therefore, the activated carbon filter 12 is connected to theenvironment via a controllable valve 13, in which case the valve 13 iscontrolled by means of the control unit 2. In addition, the activatedcarbon filter 12 is connected to the intake tract 5 of the internalcombustion engine 1 via a controllable valve 14.

Therefore, when valves 13 and 14 are in the open state, the internalcombustion engine 1 sucks in or draws in ambient air via the activatedcarbon filter 12, in which case the fuel emissions stored in theactivated carbon filter 12 are flushed and, as a result, lubricateslightly the mixture in the intake tract 5 of the internal combustionengine 1 which is measured by the lambda probe 4. Therefore, in order toflush the activated carbon filter 12, the two valves 13 and 14 are keptopen until the lambda probe 4 no longer measures any lubrication of themixture in the intake tract 5, because then all the fuel emissions havebeen flushed from the activated carbon filter 12 and in this way thestorage capacity of the activated carbon filter 12 is restored.

While the activated carbon filter 12 is being flushed, the filling ratioof the internal combustion engine 1 is increased by the fuel vaporsflushed from the activated carbon filter 12 which is connected to anincrease in performance. However, the control unit 2 compensates forthis disturbing influence of regenerating the activated carbon filter 12by adjusting the throttle valve 7 and changing the ignition angle. Inthis case, the control unit 2 takes into consideration the air ratio λmeasured by the lambda sensor 4 according to a predetermined physicalmodel into which the valve characteristic 17 of the valve 14 stored in acharacteristic element is entered, which is shown in FIG. 3 as anexample.

In addition, the fuel tank 9 has a pressure sensor 15 which measures thepressure in the fuel tank 9 and is connected to the control unit 2 inorder to evaluate the measuring signal.

Finally, another temperature sensor 16 is arranged in the fuel tank 9which measures the fuel temperature and forwards it to the control unit2. This advantageously allows a taking into consideration of thetemperature of the fuel when determining the quality of the fuel fromthe emission behavior as a result of which temperature-specificmeasuring errors are avoided.

While the internal combustion engine 1 is idling, the control unit 2carries out a calibration process in order to determine the valvecharacteristic of valve 14. Accurate knowledge of the valvecharacteristic of the valve 14 is important so that the control unit 2,while the internal combustion engine 1 is operating normally and whilethe activated carbon filter 12 is being regenerated in the case of anopen valve 14, can subsequently compensate for the disturbing influenceof the fuel vapors flushed from the activated carbon filter 12. Thecourse of this calibration process is shown in FIGS. 2 a to 2 c in theform of a flow chart and is described below.

At the beginning of the calibration process, a test is first of allcarried out to determine whether or not the calibration conditions havebeen fulfilled. This is then the case if the internal combustion engine1 is operated while it is idling because then the speed n of theinternal combustion engine 1 and the air ratio λ are regulated topredetermined desired values.

If the calibration conditions have been fulfilled, the automaticadaptation of the throttle valve position is switched off in a nextstep. Otherwise, it is necessary to wait until the calibrationconditions have been fulfilled.

The valve 14 is then closed in a next step by controlling the valve 14with a pulse-width modulated control signal with a pulse width of PW=O.

In addition, the speed n and the air ratio λ can be regulated by thecontrol unit 2 to the predetermined desired values until the desiredvalues have been reached.

The controlled variables such as the ignition angle and the position ofthe throttle valve 7 are then stored in this stationary idling operatingmode. Knowledge of the controlled variables while in the stationaryidling operating mode is important in order to be able to derivesubsequently the control deviation and the resulting valve position ofthe valve 14.

In FIG. 2 b, the pulse width PW is then increased by a predeterminedincremental value ΔPW and the valve 14 is controlled with an increasedpulse width PW.

The speed n and the air ratio λ are then again controlled until thestationary idling operating mode has been reached.

As a result, the controlled variables which are required for controllingthe disturbance are again stored.

If these new controlled variables correspond to the controlled variablesdetermined beforehand while in the stationary idling operating mode,then the filling ratio of the internal combustion engine 1 was still notincreased by the fuel vapors from the activated carbon filter 12 so thatit can be assumed that the valve 14 is still closed in the case of thepulse width PW.

The pulse width PW is then increased until the new controlled variablesdeviate significantly from the controlled variables determined at thebeginning for the stationary idling operating mode which points to anopen valve 14. The current pulse width PW is then equal to the pulsewidth PW_(MIN) in the case of which the valve 12 opens as is shown onthe basis of the valve characteristic 17 in FIG. 3.

In the steps of the calibration method according to the invention shownin FIG. 2 c, the additional course of the valve characteristic 17 isthen still determined.

For this purpose, the pulse width PW is increased progressively by theincremental value ΔPW whereby it is necessary in each case to wait untilthe speed n and the air ratio λ are regulated to the predetermineddesired values.

In this case, the controlled variables that are required to compensatefor the fuel vapors extracted or drawn off from the activated carbonfilter 12 are determined in each case.

The associated valve position Q is then determined from these controlledvariables as a result of which a support point (Q₁, PW₁) is then known.

Numerous support points of the valve characteristic 17 are thendetermined consecutively in this way until the pulse width PW exceeds apredetermined maximum value PW_(MAX).

The individual support points of the valve characteristic 17 are thenstored in a characteristic element and used while the internalcombustion engine 1 is operating normally in order to compensate for thefuel vapors flushed from the activated carbon filter 12 while theactivated carbon filter 12 is being regenerated.

The invention is not limited to the preferred embodiment describedabove. A plurality of variants and deviations that makes use of the ideaof the invention and therefore falls within the scope covered by theinvention is now possible.

1-8. (canceled)
 9. A method for controlling a regeneration valve of afuel vapor retention system for an internal combustion engine,comprising: sequentially controlling the regeneration valve withdifferent values of a control signal; regulating a speed and/or an airratio of the internal combustion engine to predetermined desired valuesfor each value of the control signal and determining the engineintervention required; deriving a valve position of the regenerationvalve from the engine intervention for each value of the control signal;and storing the individual values of the control signal and theresulting valve position as support points of a valve characteristic.10. The method as claimed in claim 9, wherein the regeneration valve ofthe fuel vapor retention system is a tank vent valve for regenerating anactivated carbon filter during which the regeneration valve iscontrolled by the control signal and the control signal corresponds to adesignated valve position of the regeneration valve and the correlationbetween the control signal and the resulting valve position of theregeneration valve is determined during a calibration process:
 11. Themethod as claimed in claim 10, further comprising; opening theregeneration valve for regenerating the fuel vapor retention system bycontrolling with a predetermined control signal; extracting or drawingoff fuel vapor from the fuel vapor retention system in the internalcombustion engine compensating for the change in the mixture compositionby the extracted or drawn off fuel vapor by means of an engineintervention; and determining the correlation between the control signaland the resulting valve position of the regeneration valve from thepredetermined control signal and the engine intervention required forthe compensation.
 12. The method as claimed in claim 11, wherein theengine intervention to compensate for the change in the mixturecomposition includes an ignition angle.
 13. The method as claimed inclaim 11, wherein the engine intervention with a view to compensatingfor the change in the mixture composition includes changing the throttlevalve position.
 14. The method as claimed in claim 11, wherein the speedof the internal combustion engine is measured and regulated to apredetermined desired value by engine intervention while the fuel vaporretention system is being regenerated.
 15. The method as claimed inclaim 11, wherein the air ratio of the exhaust gas of the internalcombustion engine is measured and regulated to a predetermined desiredvalue by engine intervention while the fuel vapor retention system isbeing regenerated.
 16. The method as claimed in claim 11, wherein theengine intervention is determined during the calibration process and iscompared to a predetermined limiting value to determine the controlsignal in the case of which the regeneration valve opens.
 17. The methodas claimed in claim 11, wherein the valve position of the regenerationvalve is determined from the engine intervention required for thecompensation.